Treatment planning system, device for calculating a scanning path and particle therapy system

ABSTRACT

In a particle therapy treatment planning system for creating treatment plan data, the movement of a target (patient&#39;s affected area) is extracted from plural tomography images of the target, and the direction of scanning is determined by projecting the extracted movement on a scanning plane scanned by scanning magnets. Irradiation positions are arranged on straight lines parallel with the scanning direction making it possible to calculate a scanning path for causing scanning to be made mainly along the direction of movement of the target. The treatment planning system can thereby realize dose distribution with improved uniformity.

CROSS-REFERENCE

This is a continuation application of U.S. application Ser. No.14/055,921, filed Oct. 17, 2013, which is a continuation application ofU.S. application Ser. No. 13/171,704, filed Jun. 29, 2011 (now U.S. Pat.No. 8,581,218), which claims priority to Japanese Patent Application No.2010-148471 filed on Jun. 30, 2010. The entire disclosures of all ofthese applications are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a treatment planning system, a devicefor calculating a scanning path and a particle therapy system,particularly the particle therapy system for treating an affected areaof a patient by irradiating the affected area with an ion beam of, forexample, protons or carbon ions and the treatment planning system usedfor a particle therapy system.

BACKGROUND OF THE INVENTION

Particle therapy is conducted by irradiating target tumor cells with aparticle beam. Among the radiant rays used in particle therapy, x raysare most widely used. Recently, however, demand has been rising forparticle therapy in which particle rays (ion beam), typically a protonbeam or a carbon ion beam capable of achieving high target doseconformity, are used.

In particle therapy, excessive irradiation or inadequate irradiation maycause adverse effects on normal tissues or may lead to recurrence of atumor. It is therefore required to irradiate a target tumor region withan ion beam for a specified dose with maximum accuracy and conformity.In the field of particle therapy, use of a scanning irradiation methodhas been increasing so as to realize high dose conformity. In a scanningirradiation method, a fine ion beam is used to completely irradiate theinside of a tumor to achieve a high dose only on a tumor region. Thescanning irradiation method does not basically require patient-specificdevices such as a collimator for forming ion beam dose distribution intoa tumor shape, so that it is possible to form dose distribution intovarious patterns.

In the scanning irradiation method, to irradiate an arbitrary positioninside a tumor, it is necessary to control the depth to which an ionbeam reaches (beam range) and the irradiation position on a planeperpendicular to the direction of beam travel (on a lateral plane). Therange of an ion beam can be controlled by varying the beam energy usingan accelerator or a range shifter. The irradiation position on a lateralplane can be arbitrarily controlled by bending the direction of beamtravel using two sets of scanning magnets.

In the scanning irradiation method, unlike in cases where an entiretumor is irradiated with spread x-rays at a time, divided regions of atumor are irradiated with a beam in turn. Therefore, when a beam isirradiated to a target which moves, for example, due to respiration orheart beat, the relative distance between irradiation positions changesto differ from the distance assumed at the time of planning, possiblymaking a planned dose distribution unavailable. In a method used toavoid the above problem, movement of an irradiation target is observedand an ion beam is irradiated only when the target is in a specificposition.

In other methods also proposed, reducing the difference between aplanned dose distribution and a real dose distribution is attempted bycontrolling the number of times of irradiation or the scanning path. Inthe method proposed in Japanese Patent No. 4273502, for example, a sametarget position is irradiated plural number of times so as to averagedose errors caused by movement of the target and thereby reduce the dosedistribution error relative to a planned dose distribution. Furthermore,according to non-patent literature (S Water, R Kreuger, S Zenklusen, EHug and A J Lomax, “Tumour tracking with scanned proton beams assessingthe accuracy and practicalities,” Phys. Med. Biol. 54 (2009) 6549-6563),aligning a main direction of ion beam scanning with the direction oftarget movement brings a real dose distribution closer to a planned dosedistribution.

SUMMARY OF THE INVENTION

With existing treatment planning systems, it has been difficult toarbitrarily set an ion beam scanning direction. In existing treatmentplanning systems, a scanning direction is determined regardless of thedirection of target movement as follows. Irradiation position control inlateral directions is performed using two sets of scanning magnets whichscan an ion beam in mutually perpendicular directions. The speeds ofscanning by the two scanning magnets are not the same. Generally, thescanning magnet positioned upstream along the direction of beam travelcan perform scanning at a higher speed. A scanning path is formed suchthat, first, scanning is made in the direction of fast scanning by oneof the scanning magnets until an end of the target is reached, then suchthat, after the scanning position is moved a little in the direction ofscanning by the other scanning magnet, fast scanning is resumed in thedirection of fast scanning. Generally, this process is repeated to forma zig-zag scanning path. This type of scanning path is formed, forexample, in the method disclosed in Japanese Unexamined PatentApplication Publication No. 2009-66106.

To scan an ion beam in the same direction as the direction of targetmovement, the treatment planning system to be used is required to graspthe movement of a target and determine a scanning direction whichcoincides with the direction of target movement. Since an ion beam canbe irradiated to a patient from an arbitrary direction by an irradiationdevice, the scanning direction has to be determined by taking intoconsideration the direction of beam irradiation even when the movementof the target is unchanged. For the operator of a treatment planningsystem, determining a scanning direction in such a situation isdifficult.

As described above, existing treatment planning systems and devices forcalculating s scanning path do not provide any means by which theoperator can specify, in a simple manner, a scanning direction takinginto consideration three-dimensional movement of a target and aspecified irradiation direction.

The above problem can be solved by the feature of the independentclaims. The dependent claims relate to advantageous embodiments of theinvention. A treatment planning system for creating a treatment plan forparticle therapy can comprising: an input device; an arithmetic devicefor performing arithmetic processing based on a result of input to theinput device and creating treatment plan information (scanning pathinformation); and a display device for displaying the treatment planinformation. In the treatment planning system, the arithmetic devicecalculates a scanning path by setting a pre-specified optional directionas a main direction for scanning irradiation positions with an ion beamusing a scanning magnet.

The arithmetic device calculates: based on multiple tomography images ofmultiple states of a target region, a position of a specific region;extracts a direction of movement of the position of the specific region;and applies the direction extracted and projected on an ion beamscanning surface as the direction of movement of the target.

With the device for calculating a scanning path according to theinvention it is possible to realize a dose distribution of a very highuniformity in the irradiation target area. According to the presentinvention, treatment planning data which can realize dose distributionwith improved uniformity can be created.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart for treatment planning according to a preferredembodiment of the present invention;

FIG. 2 is a flowchart for treatment planning by a treatment planningsystem according to a first embodiment of the present invention;

FIG. 3 is a diagram illustrating an overall structure of a particletherapy system;

FIG. 4 is a diagram illustrating a structure of a beam delivery system;

FIG. 5 is a diagram illustrating a configuration of a control systemincluding the treatment planning system according to the firstembodiment;

FIG. 6 is a diagram illustrating a structure of the treatment planningsystem according to the first embodiment;

FIG. 7 is a diagram illustrating input of a target region in a slice ofCT data;

FIG. 8 is a conceptual diagram illustrating beam irradiation by ascanning method;

FIG. 9 is a diagram illustrating a process of calculating a direction oftarget movement according to the first embodiment;

FIG. 10 is a diagram illustrating a process of calculating a directionof target movement according to the first embodiment;

FIG. 11 is a diagram illustrating a screen for specifying a direction oftarget movement by a method according to the first embodiment;

FIG. 12 is a diagram illustrating how to calculate spot positions.

FIG. 13 is a diagram illustrating a scanning direction calculated by amethod according to the first embodiment;

FIG. 14 is a diagram illustrating a coordinate system according to asecond embodiment of the present invention;

FIG. 15 is a flowchart for treatment planning by a treatment planningsystem according to a third embodiment of the present invention; and

FIG. 16 is a conceptual diagram illustrating a scanning path change madeby a method according to the third embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below withreference to drawings.

First Embodiment

A treatment planning system (or a scanning path creation system)according to a preferred embodiment of the present invention will bedescribed below with reference to drawings. First, a particle therapysystem for which the treatment planning system is used will be describedwith reference to FIGS. 3 and 4.

FIG. 3 shows an overall structure of the particle therapy system. An ionbeam generator 301 includes an ion source 302, a preaccelerator 303, andan ion beam accelerator 304. Even though the ion beam accelerator of thepresent embodiment is assumed to be a synchrotron-type ion beamaccelerator, the present embodiment is also applicable to other types ofion beam accelerators including cyclotron-type accelerators. Thesynchrotron-type ion beam accelerator 304 includes, as shown in FIG. 3,a bending magnet 305, an accelerator 306, an extraction radiofrequencydevice 307, an extraction deflector 308, and a quadruple magnet (notshown) which are arranged along the beam orbit thereof.

With reference to FIG. 3, how an ion beam generated by the ion beamgenerator 301 making use of the synchrotron-type ion beam accelerator304 is emitted toward a patient will be described below. The ionparticles (for example, protons or heavy ions) supplied from the ionsource 302 are accelerated by the preaccelerator 303 and is sent to thesynchrotron 304 that is a beam accelerator. The synchrotron 304 includesthe accelerator 306. The accelerator 306 accelerates the ion beam byapplying a radiofrequency wave to a radiofrequency acceleration cavity(not shown) provided in the accelerator 306 in synchronization with theperiod at which the ion beam circling inside the synchrotron 304 passesthe accelerator 306. The ion beam is accelerated in this way until itreaches a predetermined energy level.

When, after the ion beam is accelerated to a predetermined energy level(for example, 70 to 250 MeV), an emission start signal is outputted froma central control unit 312 via an irradiation control system 314,radiofrequency power from a radiofrequency power supply 309 is applied,by an extraction radiofrequency electrode installed in the extractionradio frequency device 307, to the ion beam circling in the synchrotron304, causing the ion beam to be emitted from the synchrotron 304.

A high energy beam transport line 310 connects the synchrotron 304 and abeam delivery system (nozzle) 400. The ion beam extracted from thesynchrotron 304 is led, via the high energy beam transport line 310, tothe beam delivery system 400 installed at a gantry 311. The gantry 311is for allowing an ion beam to be irradiated onto a patient 406 from anarbitrary direction. The gantry 311 can rotate, in its entirety, intoany direction around a bed 407 on which the patient 406 lies.

The beam delivery system 400 is for shaping the ion beam to be finallyirradiated onto the patient 406. Its structure differs depending on theirradiation method employed. A passive scattering method and a scanningmethod are among typical irradiation methods. The present embodimentuses the scanning method. In the scanning method, a fine ion beamtransported through the high energy beam transport line 310 isirradiated as it is onto a target and is scanned three-dimensionallymaking it possible to consequently form a high dose region on the targetonly.

FIG. 4 shows a structure of the beam delivery system 400 employing thescanning method. The roles and functions of components of the beamdelivery system 400 will be briefly described below with reference toFIG. 4. The beam delivery system 400 is provided with scanning magnets401 and 402, a dose monitor 403, and a beam position monitor 404arranged in the mentioned order from the upstream side. The dose monitormeasures the amount of the ion beam passing therethrough. The beamposition monitor can measure the position passed through by the ionbeam. The information provided by these monitors enables the irradiationcontrol system 314 to perform control to keep the ion beam irradiated toa predetermined position in a predetermined amount.

The direction of travel of the fine ion beam transported from the ionbeam generator 301 through the high energy beam transport line 310 isbent by the scanning magnets 401 and 402. These scanning magnets areprovided so as to cause magnetic flux lines to be generatedperpendicularly to the direction of travel of the ion beam. Referring toFIG. 4, for example, the scanning magnet 401 bends the ion beam in ascanning direction 405 and the scanning magnet 402 bends the ion beamperpendicularly to the scanning direction 405. Using these two scanningmagnets, the ion beam can be moved to an arbitrary position in a planeperpendicular to the direction of travel thereof so as to irradiate atarget 406 a.

The irradiation control system 314 controls, via a scanning magnet fieldstrength control device 411, the amounts of current applied to thescanning magnets 401 and 402. The scanning magnets 401 and 402 havecurrents supplied from scanning magnet power supplies 410 allowingmagnetic fields of strengths corresponding to the amounts of currentssupplied to be generated so as to arbitrarily set the degree of bendingof the ion beam. The relationships between the ion beam, degree of beambending, and amounts of currents are held as a table in a memory 313included in the central control unit 312 to be referred to as required.

When the scanning method is used for ion beam irradiation, an ion beamcan be scanned in two ways. In one way, discrete scanning is made inwhich an irradiation position is moved and stopped repeatedly. In theother way, an irradiation position is continuously changed. In discretescanning, a predetermined amount of ion beam is irradiated at a fixedposition which is referred to as a spot. Supply of the ion beam is thensuspended and the amounts of currents applied to the scanning magnetsare changed so as to move the irradiation position. After theirradiation position is moved, irradiation of the ion beam is resumed.When, in this process, high-speed scanning is possible, the ion beamneed not necessarily be suspended.

In the method in which the ion beam irradiation position is continuouslymoved, the irradiation position is changed while irradiation of the ionbeam is maintained. Namely, the irradiation position is changed bycontinuously changing the degrees of excitation of the scanning magnetswhile the ion beam irradiation is maintained so as to scan the entirepart of the irradiation field. In this method, the irradiation amountcan be changed over different irradiation positions by changing eitheror both of the speed of scanning effected by the scanning magnets andthe amount of ion beam current.

A treatment planning system according to a preferred embodiment of thepresent invention will be described below with reference to FIG. 5. Atreatment planning system 501 is connected, via network, to a dataserver 502 and the central control unit 312. The treatment planningsystem 501 includes, as shown in FIG. 6, an input device 602, a displaydevice 603, a memory 604, an arithmetic processing unit 605, and acommunication device 606. The arithmetic processing unit 605 isconnected to the input device 602, display device 603, memory (storagedevice) 604, and communication device 606.

Prior to treatment, images for use in treatment planning are taken. Asimages used for treatment planning, computed tomography (CT) data ismost popular. CT data used for treatment planning is three-dimensionaldata composed using images of a patient taken by irradiation from pluraldirections. With image taking growing higher in speed recently, computedtomography makes it possible to acquire plural sets of CT data on pluralstates (referred to as phases) of even a patient's site periodicallymoving due to respiration by taking plural images of the site indifferent phases caused by respiratory movement. This computedtomography is referred to as four-dimensional computed tomography(4DCT). 4DCT imaging makes it possible to observe movement due to, forexample, respiration of a target by comparing CT data on differentphases of the site. When using such a method, to make movement of thetarget observable with increased accuracy, a marker such as a metal ballmay be implanted in the target.

CT data taken using a CT system (not shown) is stored in the data server502. The treatment planning system 501 uses the CT data. FIG. 1 is aflowchart for treatment planning. When treatment planning is started(step 101), the treatment planning system 501 reads required CT datafrom the data server 502 in accordance with instructions from a medicalphysicist (or doctor) operating the treatment planning system 501.Namely, the treatment planning system 501 copies (stores) the CT datafrom the data server 502 to the memory 604 via the network connected tothe communication device 606.

When the CT data has been read, the operator, while checking the CT datadisplayed on the display device 603, inputs data on a region to bespecified as a target for each slice of the CT data using the inputdevice 602 that may be, for example, a mouse. When, like in the case of4DCT, there are plural data sets acquired by imaging a same site, animage may be synthesized from plural images and the above targetselection operation may be performed using the synthesized image. A setof synthesized image can be obtained, for example, by comparing the CTvalues of each set of corresponding spots, each representing a sameposition, of plural images and selecting a highest luminance value foreach position.

When region data has been inputted for each slice of the CT data, theoperator registers the inputted regions in the treatment planning system(step 102) causing the regions inputted by the operator to be stored asthree-dimensional position information in the memory 604. In cases wherethere are other regions to be also assessed and controlled, for example,when there are critical organs requiring doses on them to be minimized,the operator also registers the positions of such critical organs. FIG.7 shows a state with a target region 702 inputted, by an operator usingthe display device 603, on a slice 701 including CT data.

Next, the operator specifies the direction of irradiation that isdetermined by the angles of the gantry 311 and bed 407. For irradiationfrom plural directions, specify plural sets of angles. The otherparameters to be determined by the operator to perform ion beamirradiation include the dose (prescription dose) to be irradiated oneach region registered in step 102 and the distance between adjacentspots. The prescription doses to be determined as irradiation parametersalso include, besides the dose to be irradiated on each target, atolerable dose for each critical organ. The distance between adjacentspots is initially determined automatically to be approximately the sameas the beam size of the ion beam, but it can be changed by the operator.The operator is required to set these irradiation parameters (step 103).

In addition to the above parameters, the direction of target movement isspecified using a feature function of the treatment planning systemaccording to the present embodiment. How to specify the direction oftarget movement will be described below with reference to FIGS. 8 and 9.As shown in FIG. 8, for ion beam irradiation, the gravitational centerof the target region 702 is assumed to be positioned to coincide with anisocenter (rotational center of the gantry 311) 801. A spot position isdefined on coordinates in a plane (isocenter plane) 804 perpendicular toa straight line (beam center axis) 803 which includes the isocenter 801and connects a scanning center (beam source) 802 and the isocenter 801.In the following, the plane 804 will be referred to as the isocenterplane and the straight line 803 will be referred to as the beam centeraxis. For example, when there is a spot at position 805 on the isocenterplane 804, the currents applied to the scanning magnets 401 and 402 areadjusted to make the ion beam pass the position 805 on the isocenterplane 804. As a result, the trajectory of the ion beam becomes like astraight line 806. How far the ion beam reaches depends on the beamenergy.

The following description will be based on an example case in which 4DCTdata is taken making use of an implanted marker. Effects similar tothose generated in the following example case can also be obtainedwithout using any marker by having an arbitrary feature point in animage specified by the operator. The treatment planning system 501searches all CT slice images provided by the 4DCT data for each phasestored in the memory 604 and determines a marker position in each slice.This may be done directly by the operator when automatic searching isdifficult. Consequently, the marker position in the CT data for eachphase is determined. This process is illustrated in FIG. 9. In FIG. 9,points 902 and 903 each represent a marker position in a phase. Linearlyconnecting the marker positions in all phases determines athree-dimensional marker trajectory 904. The marker is positioned suchthat the marker trajectory represents movement of a target.

Next, the marker positions, including the points 902 and 903, in allphases are projected on the isocenter plane 804. In FIG. 9, point 905represents the point 902 projected on the isocenter plane 804. Thus,projecting all marker positions on the isocenter 804 determines a markertrajectory 906 projected on the isocenter plane 804.

The projection result is displayed on the display device 603 of thetreatment planning system 501. This is illustrated in FIG. 10. Points1001, 1002, 1003, 1004, 1005, and 1006 represent the marker positions incorresponding phases projected on the isocenter plane 804. Based on thedisplayed marker positions, the arithmetic processing unit 605 of thetreatment planning system 501 automatically calculates the direction oftarget movement. For example, the arithmetic processing unit 605calculates the distances between multiple points 1001 to 1006 anddetermines two points, the distance between which is larger than thedistance between any other combined two points. In the case of theexample shown in FIG. 10, points 1001 and 1004 are selected as the twopoints most spaced apart and the direction along line 1007 connectingpoints 1001 and 1004 is defined as the direction of target movement. Incases where an ion beam is emitted only when the marker is inside aspecific region, it is possible to extract only the points correspondingto the phases with the marker in such a specific region and performcalculations as described above.

The direction of target movement determined by calculation is alsodisplayed on the display device 603 of the treatment planning system501. An example of the direction display is shown in FIG. 11. In FIG.11, an arrowed direction 1101 represents the calculated direction oftarget movement. This display appears together with a display of theisocenter plane 804 shown in FIG. 10. Or, the arrow 1101 may bedisplayed overlapped with a display like the one shown in FIG. 10. Thecoordinate systems 1008 shown in FIGS. 10 and 1102 shown in FIG. 11 bothused to define directions are common. The operator can manually modify,as required, the direction referring to the coordinate systems. Namely,the direction can be changed by inputting, on the input screen 1103, anx-direction component and a y-direction component of the arrow 1101. Itis also possible to directly change the arrow direction on the displayscreen using an input device such as a mouse (step 104).

The direction of target movement may be determined after markerpositions are projected on a plane as described above, but it may alsobe determined without projecting marker positions. Namely, referring toFIG. 9, out of all the points including points 902 and 903, two thedistance between which is longer than the distance between any othercombination of two points are selected and the direction along a lineconnecting the selected two points is determined as the direction oftarget movement. In the example case shown in FIG. 9, the directionalong a line connecting points 902 and 903 is determined as thedirection of target movement. Projecting the direction thus determinedon the isocenter plane 804 determines the direction of target movementon the isocenter plane.

An advantage of the above method of determining the direction of targetmovement without projecting marker positions on a plane is thatcomponents of target movement in a direction perpendicular to theisocenter plane 804 can also be calculated. The dose distribution causedby an ion beam becomes a Gaussian-like distribution along a directionperpendicular to the direction of travel of the ion beam. The dosedistribution along the direction of travel of the ion beam, however,shows a sharp peak immediately before the ion beam stops. Generally,therefore, the movement of a target along the direction of travel of theion beam, i.e. a direction perpendicular to the isocenter plane 804,affects the dose distribution more than the movement of a target along alateral direction. When the component of target movement in a directionperpendicular to the isocenter plane 804 is also displayed on thedisplay screen shown in FIG. 11, the operator can modify the directionof beam irradiation that is determined by the angles of the gantry 311and bed 407 so as to make the component of target movement perpendicularto the isocenter plane 804 smaller than a maximum allowable value.

After the above parameters are determined, the treatment planning system501 automatically performs calculations (step 105). In the following,details of calculations the treatment planning system 502 performsfollowing the flowchart shown in FIG. 2 will be described.

First, the treatment planning system 501 determines positions to beirradiated with an ion beam. In cases where a discrete scanning methodis used, discrete spot positions are calculated. In cases where an ionbeam is to be irradiated continuously, a scanning path is calculated.Even though, the following description of the present embodiment isbased on a discrete scanning method, a continuous scanning method mayalso be used. Effects similar to those of the present embodiment canalso be obtained using a continuous scanning method which can beregarded as a method in which discrete positions to be irradiated withan ion beam are very closely arranged along a scanning path. When pluralirradiation directions (determined by the angles of the gantry 311 andbed 407) are specified, the operation performed for a single irradiationdirection is repeated for the plural irradiation directions.

The treatment planning system 501 starts selecting spot positions basedon the CT data stored in the memory 604 and the region informationinputted by the operator (step 201). As described in the foregoing, thepositions to be irradiated with an ion beam are determined on thecoordinates on the isocenter plane 804. Referring to FIG. 8, assume thatthe point 805 on the isocenter plane 804 is selected as a position to beirradiated. The treatment planning system 501 seeks an energy levelwhich, when an ion beam is irradiated along the straight line 806connecting the beam source 802 and point 805, causes the ion beam tostop approximately in a target range and selects the energy level (notnecessarily singular) for use in irradiating the point 805. This processfor energy level selection is performed for every irradiation positionset on the isocenter plane. As a result, the combinations of positionsto be irradiated on the isocenter plane and energy levels to be used aredetermined. In this way, the spots to be actually irradiated with an ionbeam are determined.

On the isocenter plane 804, the positions to be irradiated are selectedsuch that the distance between adjacent positions does not exceed thevalue specified in step 103. In an easiest way, positions may bearranged to form a square lattice such that positions mutually adjacentalong a side are spaced apart from each other by a predetermineddistance along the side. The treatment planning system 501 of thepresent embodiment can select the direction determined in step 104 asthe axis of the above lattice, i.e. as the direction along which thepositions to be irradiated are linearly arranged. FIG. 12 is aconceptual illustration of the process leading to selection of spots.The direction 1101 determined in step 104 is also shown in FIG. 12.

The treatment planning system 501 first sets plural straight linesparallel with the direction 1101 (step 202). Straight line 1201represents one of the plural straight lines. The straight lines arespaced apart by the distance selected in step 103. Next, irradiationpositions are set on each of the plural straight lines (step 203). Thedistance between irradiation positions adjacent to each other on a samestraight line equals the distance between straight lines adjacent toeach other. In FIG. 12, the irradiation positions thus set, including1202 and 1203, are circularly represented, and it is seen that they arearranged to form a square lattice with its axis represented by thedirection 1101. Finally, a beam energy level which causes, when theirradiation positions are irradiated with an ion beam, the ion beam tostop inside the target range is selected (step 204). The irradiationpositions for which the ion beam stops outside the target range are notirradiated with the ion beam. Referring to FIG. 12, the irradiationpositions, including 1202, represented by white circles are notirradiated with the ion beam. Only the irradiation positions, including1203, represented by black circles, are irradiated with the ion beam.Broken line 1204 represents the target range contour at the depth wherethe ion beam of a certain energy level stops.

In cases where scanning is performed discretely and ion beam emission issuspended during the time after a spot is irradiated with an ion beamuntil the next spot starts being irradiated, the consequential dosedistribution is not dependent on the scanning path. In such cases, thescanning path may be determined after the dose is determined for eachspot. In the present embodiment, however, the scanning path isdetermined at this stage with consideration that, when a differentscanning method is adopted, it becomes necessary to calculate dosedistribution taking into consideration the scanning path. Namely, in thepresent embodiment, the scanning path is determined in step 205regardless of the scanning method to be used.

The scanning path is determined to be along the straight lines set instep 202. Referring to FIG. 13, the spots, including point 1203, to beirradiated with a certain beam energy level are represented by blackcircles. The scanning path begins with the straight line 1301 that isthe top line among the straight lines set to be parallel with thedirection defined by the operator. The ion beam scanning advances fromspot to spot first along the straight line 1301. When the last spot onthe straight line 1301 is reached, scanning moves to the next straightline adjacent to the straight line 1301 and the direction of scanning isreversed. This process is repeated until all the spots on straight line1302 have been scanned. Consequently, the scanning path is zigzagged asindicated by arrow 1303.

The operation for determining a scanning path is performed for the spotsto be irradiated with each of the selected beam energy levels. When theoperation is completed for every energy level, the scanning paths forall spots to be irradiated have been determined (step 206). This isrepeated for every irradiation direction in cases where irradiation isto be made in plural directions (step 207).

When all spot positions and a scanning path for them have beendetermined, the treatment planning system 501 starts calculation forirradiation amount optimization (step 208). This calculation determinesthe irradiation amount for each spot so as to approach the target dosedistribution set in step 103. For this type of calculation, an objectivefunction is widely made use of. The objective function represents anerror quantified relatively to a target dose distribution determinedusing spot-by-spot irradiation amounts as parameters. The objectivefunction is defined such that its value is smaller when the target dosedistribution is approached closer. An irradiation amount for each spotwhich minimizes the function value is sought by iterative calculationand is determined as an optimum irradiation amount.

When the irradiation amount for each spot has been determined throughiterative calculation, the treatment planning system 501 calculates dosedistribution based on the finalized spot positions and spot irradiationamounts (step 209). The calculation results are displayed on the displaydevice 603 (step 210). The operator checks the calculation results anddetermines whether the dose distribution meets the target conditions.Not only the dose distribution but also the spot positions and scanningpath calculated by the treatment planning system 501 can also be checkedon the display device 603 (step 106). When the dose distribution or thescanning path is found undesirable, the operator returns to step 103 andchanges the settings of irradiation parameters such as the irradiationdirection, prescription dose, or distance between spots.

Even when the operator returns to step 103 and changes parametersettings, the direction of target movement determined in step 104 isretained. According to the new conditions specified by the operator, thescanning path and the dose distribution are updated through steps 201and 209, and the new results are displayed on the display device 603.When the displayed results are determined desirable, treatment planningis finished (step 107). The irradiation conditions acquired are stored,via network, in the data server 502 (steps 108 and 109).

When irradiating an ion beam, the central control unit 312 reads thecorresponding treatment planning data stored in the data server 502. Ifnecessary at that time, the data can be converted into a format readableby the central control unit 312. The central control unit 312 specifiesconditions for ion beam irradiation such as the ion beam energy to beirradiated, scanning positions, and irradiation amounts. The irradiationcontrol system 314 irradiates an ion beam based on the conditionsspecified by the central control unit 312.

According to the present embodiment, it is possible to input movement ofa patient's affected area and generate treatment planning data to causean ion beam to be scanned mainly in a direction coinciding with thedirection of the movement, so that treatment planning data which canrealize dose distribution with improved uniformity can be provided.

Second Embodiment

Even though, in the first embodiment, the direction of target movementis extracted using 4DCT images, effects similar to those of the firstembodiment can also be obtained according to a second embodiment of theinvention by having the direction of target movement directly specifiedby the operator using ordinary CT data without using any 4DCT image. Thesecond embodiment will be described below.

The operation according to the second embodiment is the same as in thefirst embodiment up to step 103 shown in FIG. 1. The operation differingfrom the first embodiment will be described in the following. In thesecond embodiment, the direction of target movement is determined, instep 104, by the operator without using any 4DCT data. In cases wherethe direction of movement of a specific organ caused, for example, byrespiration or heart beat is not considered to vary much, the operatormay directly specify the direction of target movement without checkingthe target position, for example, using a marker, i.e. saving theoperation for extracting the direction of target movement.

The operator specifies the direction of target movement in athree-dimensional coordinate system, for example, like the one shown inFIG. 14, based on CT data. In FIG. 14, the foot-to-head direction isdefined as z axis, and x and y axes are set to be perpendicular to the zaxis, respectively. When the target is determined to move in thefoot-to-head direction, the operator specify a three-dimensionaldirection in the coordinate system. For example, the operator inputscoordinate value (x, y, z)=(0, 0, 1) from an input screen like the oneshown in FIG. 11.

When the direction of target movement is determined, the treatmentplanning system projects the direction specified in the coordinatesystem shown in FIG. 14 on the isocenter plane 804 and calculates thedirection projected on the isocenter plane 804. When the direction onthe isocenter plane 804 is determined, the operation of and subsequentto step 105 can be performed in the same way as in the first embodiment.Since the present embodiment requires no marker position to bedetermined for each phase, the operation to be performed by the operatoris reduced.

According to the present embodiment, it is possible to input movement ofa patient's affected area and generate treatment planning data to causean ion beam to be scanned mainly in a direction coinciding with thedirection of the movement, so that treatment planning data which canrealize dose distribution with improved uniformity can be provided.

Third Embodiment

In the first and second embodiments, spots are arranged on straightlines parallel with a specified direction. In that way, when thespecified direction is changed, the spot positions are also changedmaking it necessary to perform the operations beginning with step 203shown in FIG. 2.

When a discrete scanning method in which ion beam irradiation is stoppedduring scanning is used, the dose distribution is not dependent on thescanning path as long as the spot positions remain unchanged. In thiscase, it is possible, unlike in the first and second embodiments, tochange only the scanning path portion that begins at a predeterminedspot into an arbitrary direction. Such a method will be described belowas a third embodiment.

FIG. 15 shows the flow of operation, according to the third embodiment,corresponding to the automatic calculation performed by the treatmentplanning system 501 (step 105 shown in FIG. 1). After automaticcalculation is started (step 1501), spot positions are selected (step1502), the irradiation amount is optimized for each spot (step 1503),and dose distribution is calculated (step 1504) as done by an existingtreatment planning system without taking the scanning direction intoconsideration.

In the method of the present embodiment, the scanning path is changedafter dose distribution is calculated in step 1504. First, the directionof target movement specified in step 104 shown in FIG. 1 is read (step1505). Subsequently, a scanning path is set as described below for spotsto be irradiated with a same level of beam energy and from a sameirradiation direction (step 506). When a scanning path is specified, thearithmetic processing unit 605 of the treatment planning system 501prepares a function for converting the path into an appropriate value.For example, the function may be defined based on the total scanningdistance along the scanning path such that its value is smaller when thescanning direction is closer to the direction specified in step 104. Outof various scanning paths, the one that makes the value of the definedfunction smallest is searched for, for example, using a simulatedannealing algorithm, as an optimum scanning path.

An example is shown in FIG. 16 in which reference numeral 1601represents a state with an unchanged scanning path for spots to beirradiated with a same level of beam energy. Spot positions arerepresented by black circles and an arrow 1602 represents an initialscanning path. The scanning path 1602 has been set without taking intoconsideration the direction of target movement. Reference numeral 1603represents a state with a scanning path changed based on a specifieddirection of target movement. The spot positions are not differentbetween the two states. In the state 1603, however, a direction oftarget movement 1604 is specified and it is seen that a scanning path1605 has been set to cause scanning to proceed mostly along thespecified direction.

This is performed for every level of beam energy to be irradiated andevery irradiation direction (determined by the angles of the gantry 311and bed 407) (steps 1507 and 1508). Finally, the irradiation parametersincluding the scanning path information thus determined are outputtedand the operation is ended (steps 1509 and 1510).

In the method of the present embodiment, the scanning path can bechanged after the spot positions and the irradiation amount for eachspot are determined. The scanning path can therefore be changed outsidethe treatment planning system. For example, there can be a case in whichthe scanning path is changed using the central control unit 312immediately before ion beam irradiation. The treatment planning datagenerated by the treatment planning system 501 is stored in the dataserver 502. In performing ion beam irradiation, the data stored in thedata server 502 is read by the central control unit 312. At that time,the central control unit can display the scanning path on the displaydevice 315 and provide an interface for changing the scanning path,thereby allowing the operator to change the scanning path using an inputdevice (not shown) provided for the central control device. By inputtinginstructions for changing the scanning path on a screen like the oneshown in FIG. 11 or in a coordinate system like the one shown in FIG.14, the operator can change the scanning path as done in step 1506.

According to the present embodiment, an ion beam scanning path can bechanged by observing the state of a target immediately before startingion beam irradiation, so that the movement of the target to beirradiated can be well reflected in treatment to be performed. Eventhough a scanning path can be changed immediately before starting ionbeam irradiation by the methods of the first and second embodiments,too, the method of the present embodiment makes it possible to changeonly the scanning path without affecting the dose distribution. Thus,the present embodiment has advantages in that the scanning path can bechanged requiring less time for calculation and in that advisability ofthe treatment plan after a change in the dose distribution can bechecked (step 107) in a simple manner.

According to the present embodiment, it is possible to input movement ofa patient's affected area and generate treatment planning data to causean ion beam to be scanned mainly in a direction coinciding with thedirection of the movement, so that treatment planning data which canrealize dose distribution with improved uniformity can be provided.

What is claimed is:
 1. A particle therapy system comprising: an ion beamaccelerator; at least one device receiving direction informationreferring to target movement; and an irradiation control systemcontrolling ion beam irradiation, a scanning direction of the ion beamirradiation being determined based on the received direction informationreferring to target movement.
 2. A particle therapy system comprising:an ion beam accelerator; at least one device receiving, from anoperator, direction information of ion beam irradiation; and anirradiation control system controlling the ion beam irradiation, the ionbeam irradiation being scanned along the received direction informationof ion beam irradiation.
 3. The particle therapy system according toclaim 1, wherein the ion beam irradiation is scanned along the receiveddirection information projected on an isocenter plane.
 4. The particletherapy system according to claim 1, wherein the direction informationreceived by the at least one device being a direction of movement of aspecific organ caused by respiration or heartbeat, wherein theirradiation control system scans the ion beam irradiation mainly in adirection coinciding with the received direction information of theorgan movement.
 5. The particle therapy system according to claim 1,further comprising a display device displaying a dose distributioncalculated based on a certain spot position and a scanning path, thedisplay device displaying an input screen enabling manually modifyingthe scanning direction of the ion beam irradiation.
 6. The particletherapy system according to claim 1, further comprising a deviceenabling a modification of the ion beam irradiation direction, themodification making a component of the received direction perpendicularto an isoplane smaller.
 7. The particle therapy system according toclaim 2, wherein the ion beam irradiation is scanned along the receiveddirection projected on an isocenter plane.
 8. The particle therapysystem according to claim 2, further comprising a display devicedisplaying a dose distribution calculated based on a certain spotposition and a scanning path, the display device displaying an inputscreen enabling manually modifying the scanning direction of the ionbeam irradiation.
 9. The particle therapy system according to claim 2,further comprising a device enabling a modification of the ion beamirradiation direction, the modification making a component of thereceived direction perpendicular to an isoplane smaller.
 10. Theparticle therapy system according to claim 2, wherein the irradiationcontrol system scans the ion beam irradiation mainly in a directioncoinciding with the received direction information.